Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.

Pioneer 11, the sister spacecraft to Pioneer 10, was the first human-made object to fly past Saturn and also returned the first pictures of the polar regions of Jupiter.

After two midcourse corrections (on 11 April 1973 and 7 November 1974), Pioneer 11 penetrated the Jovian bow shock on 25 November 1974. The spacecraft's closest approach to Jupiter occurred at 05:22 UT on 3 December 1974 at a range of 42,760 kilometers from the planet's cloud tops, three times closer than Pioneer 10.

It was traveling faster than any human-made object at the time-171,000 kilometers per hour. Because of its high speed during the encounter, the spacecraft's exposure to radiation was much less than that of its predecessor. Pioneer 11 repeatedly crossed Jupiter's bow shock, indicating that the Jovian magnetosphere changes its boundaries as it is buffeted by the solar wind.

Pioneer 11 used Jupiter's massive gravitational field to swing back across the solar system to set itself on a flyby course with Saturn. After its Jupiter encounter, on 16 April 1975, the micrometeoroid detector was turned off because it was issuing spurious commands that were interfering with other instruments.

Pioneer 11 detected Saturn's bow shock on 31 August 1979, about 1.5 million kilometers out from the planet, thus providing the first conclusive evidence of the existence of Saturn's magnetic field. The spacecraft crossed the planet's ring plane beyond the outer ring at 14:36 UT on 1 September 1979 and then passed by the planet at 16:31 UT for a close encounter at a range of 20,900 kilometers. It was moving at a relative speed of 114,100 kilometers per hour at the point of closest approach.

Among Pioneer 11's many discoveries was a narrow ring outside the A ring named the "F" ring and a new satellite 200 kilometers in diameter. The spacecraft recorded the planet's overall temperature at -180°C and photographs indicated a more featureless atmosphere than that of Jupiter. Analysis of data suggested that the planet was primarily made of liquid hydrogen.

After leaving Saturn, Pioneer 11 headed out of the solar system in a direction opposite to that of Pioneer 10-that is, to the center of galaxy in the general direction of Sagittarius. Pioneer 11 crossed the orbit of Neptune on 23 February 1990, thus becoming the fourth spacecraft (after Pioneer 10 and Voyagers 1 and 2) to do so.

By 1995, 22 years after launch, two instruments were still operational on the vehicle. NASA Ames Research Center finally terminated routine contact with the spacecraft on 30 September 1995. Scientists received a few minutes of good engineering data on 24 November 1995 but lost final contact once Earth permanently moved out of view of the spacecraft's antenna.

Like Pioneer 10, Pioneer 11 carries a plaque with a message for any intelligent beings that might find it.

Key Dates

5 Apr 1973: Launch (02:11 UT)

3 Dec 1974: Jupiter Flyby

1 Sep 1979: Saturn Flyby

24 Nov 1995: Final Contact

Status: Successful

Fast Facts

Both Pioneer 10 and 11 carry a plaque describing the spacecraft, human beings and the location of our solar system.